How the calculator counts materials
A wood fence is a row of sections. Each section spans from one post to the next and carries the rails and pickets (or a pre-built panel). Once you know the number of sections, the rest follows.
- Sections. For each side, take its length (minus any gate openings), divide by the post spacing and round up. Partial sections still need a full set of posts and rails.
- Posts. A straight run needs one more post than it has sections. Where two sides meet at a corner they share one post, and a closed loop shares every corner. Each gate splits a run, so it adds one post, and the two posts on either side of the opening become gate posts.
- Pickets. Fence length in inches divided by the actual picket width, plus the gap for a spaced fence.
- Rails. Sections times rails per section. Taller privacy fences often use three.
- Concrete. For each hole, the cylinder volume (π × radius² × fill depth) minus the space the post takes up. Divide the total by the bag yield on the label and round up.
Worked example
A backyard fence runs 50 feet, 100 feet and 50 feet, meeting at two corners, with the house closing the fourth side. It is 6 feet tall, with one 4-foot gate, posts 8 feet apart and 5½-inch privacy pickets on three rails.
- Fence length: 200 feet minus the 4-foot gate = 196 feet
- Sections: 7 + 12 + 7 = 26 (the 96 feet left on the long side divide into 12)
- Posts: 26 sections + 3 runs − 2 shared corners + 1 for the gate = 28 posts, two of them gate posts
- Pickets: 196 × 12 ÷ 5.5 = 428, or 471 with 10% extra
- Rails: 26 × 3 = 78
- Concrete: a 10½-inch hole for a 3½-inch post, filled 33 inches deep (36-inch hole, 3 inches left at the top), holds about 1.42 cubic feet. 28 holes need 39.8 cubic feet, or 73 bags of 80-lb mix with 10% extra.
That is nearly 1.5 cubic yards and close to three tons of bags, which is why bigger fence jobs sometimes order ready-mix or rent a mixer. The concrete calculator compares both.
| Product | Bag | Yield per bag | Bags per cubic foot |
|---|---|---|---|
| Concrete Mix | 40 lb | ≈0.30 ft³ | 3.3 |
| Concrete Mix | 60 lb | ≈0.45 ft³ | 2.2 |
| Concrete Mix | 80 lb | ≈0.60 ft³ | 1.7 |
| Fast Setting Concrete Mix | 60 lb | ≈0.45 ft³ | 2.2 |
Post holes: the starting rule and the real rule
Quikrete's fast-setting concrete instructions give a simple starting point: make the hole three times as wide as the post and half as deep as the post's height above ground, then fill with dry mix to about 3 to 4 inches from the top before adding water. For a 6-foot fence that means a 36-inch hole and posts at least 9 feet long.
Your local building code, frost depth, soil and wind exposure can require something different, and some towns limit fence height or require a permit. A homeowner association may also control style and color. Check before you buy posts, because post length depends on hole depth.
Edge cases
- Panels: set post spacing to match how your panels attach (center to center, usually the panel width plus the post width for panels that mount between posts), or they will not line up.
- Gate position: the calculator takes gate openings out of the longest side and counts that side as one run. Depending on where the gate sits, the two pieces on either side of it can need one more section than the total suggests.
- Slopes: stepped or racked fences on a slope use the horizontal length for posts but may need extra pickets and longer posts on the low side.
- Property line: confirm where it is from your survey or deed before you set posts. The ACRIS guide shows how to find NYC deed records.
What to do next
Price the list at two suppliers, then add hardware, gravel and stain. If the fence borders a new deck, the deck calculator counts boards, joists and footings, and the home maintenance budget calculator helps plan for upkeep.